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### Chapter 2

Scientific Method

Scientific Method

- Scientific method- logical approach to solving problems by observing & collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data
- Examples of problems…
- Observable data
- Qualitative = descriptive (turn pink)
- Quantitative = numerical (1 gram)

Data

- We cannot observe everything all at once, so we focus on a system
- System- specific portion of matter chosen for study (ex. Reaction in a test tube)
- Once we obtain data, we can establish patterns
- Patterns can be made into scatter plots, bar graphs, pie charts, etc.

Hypothesis

- Once we have looked for patterns, we form a hypothesis
- Hypothesis- testable statement in the form of “if…then…”
- Then we have to test the hypothesis
- Control(s)- stay constant (placebo)
- Variable(s)- change, only changed one at a time
- If wrong, change or drop hypothesis (might start over)

Hypothesis (con.)

- If correct, explain through models
- Model- explains how events occur or are related in a visual, verbal, or mathematical way
- Theory- broad generalization that explains group of facts or events
- Publish results (letters, scholarly journals, blog, word of mouth)

Metric System

- SI, or SystèmeInternationaled’Unités (French)
- Base units
- Length (lowercase L) = meter (m)
- Mass (m) = kg (kilogram)
- Time (t) = second (s)
- Temperature (T) = Kelvin (K)
- Amount of substance (n) = mole (mol)
- Electric current (I) = ampere (A)
- Luminous intensity (Iv) = candela (cd)

Metric prefixes

- Mega (M) = 10 6
- Kilo (k) = 10 3
- Hecto (h) = 10 2
- Deka (da) = 10 1
- Deci (d) = 10 -1
- Centi (c) = 10 -2
- Milli (m) = 10 -3
- Micro (µ) = 10 -6
- Practice problems on board

Mass vs. Weight

- Mass = amount of matter
- Weight = amount of gravity pull
- On moon, gravity 1/6 that of Earth
- Didn’t lose mass, lost weight

Derived SI units

- Combinations of base units
- Area (A) = lxw = m2 or cm2
- Volume (V) = lxwxh = m3 or cm3
- Density (D) = kg/m3 or g/cm3 or g/mL
- Molar Mass (MM) = kg/mol
- Energy (E) = Joule (J)

Accuracy vs. Precision

- Accuracy- close to accepted value
- Precision- close to measurements made in same way
- Drawings on board

Percent Error

- Goal = 0
- (Experimental – Accepted)/(Accepted) x 100
- Problems on board

Significant figures

- All digits but last one certain
- Rules
- Nonzero = significant
- Zero in between nonzero (2002) = significant
- Zero in front of nonzero = not significant
- Zero at end of number and to right of decimal = significant
- Ex. 2000 = 1 sig, 25.00 = 4 sig, .0001 = 1 sig
- Examples on board

Rounding

- 1->4, round down
- 6->9, round up
- 3.5->4
- 4.5->4
- Sig + or – Sig= same # of decimals
- Sig x or / Sig = same # of sig digits
- Examples on board

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